In communications and data transmission it is known to assemble and transmit recurrent data frames of information from a central distribution location to a plurality of destination stations, the frames each containing a plurality of packets, each packet or group of packets having a unique destination identifier. The packets are assembled such that data following an ID identifier are received by the identified destination station, decoded and then delivered to a service subscriber's instrument.
One transmission signal format commonly encountered in conventional telephone wire systems is known as T1, which is a 24 channel time division multiplexed signal format in which each frame increment comprises a 125 microsecond interval (8 Kilohertz sampling rate). The present invention has utility in both electrical and optical transmission systems, and in systems which deliver only voice, only data, or only video information, or combinations thereof. Since a preferred embodiment of the invention is for use in optical fiber transmission systems, reference to such networks will be made throughout this description in explaining the invention though it should be understood that the invention is not limited to that single application. In modern optical fiber networks it has been decided to follow the conventional 125 microsecond frame interval for forming information frames for transmission over an optical fiber network.
Prior approaches for framing voice/data packets include synchronous and asynchronous methods. For framing synchronous transmissions, it is conventional for network units which are to receive the information to include counters which are set to zero at a beginning of a frame and count a preset number of units or bytes after the beginning of the frame to determine when bytes or packets for that particular units are to be received and decoded. With this approach, each packet does not need to have a unique destination identifier associated with it. This approach is disadvantageous since it is difficult to remotely program the network units over time to change a number of bytes each network unit is to receive. This approach is thus inefficient in terms of providing flexibility needed to adapt to changing subscriber needs and network needs, and basically requires a relatively complicated circuit implementation. For example, it is not uncommon that after a network has been operating that additional network units are added to the network, or for any network unit or any user being served thereby may require additional or less bandwidth to accommodate additional or less equipment acquired or discarded after network initialization.
To address these needs, it has also been proposed to transmit data asynchronously in packets each having a destination identifier so that any network unit can easily and efficiently determine which packets are intended for it so that packet fields for any network unit can be contracted or enlarged "on the fly". In addition, transmitting asynchronously allows each frame to optimally have a dark period during which no information is being transmitted which provides flexibility necessary when new network units are added to the network after system initialization.
Thus, a heretofore unsolved need has been for an improved and simplified method for formatting frames for distribution from a network host terminal to network units to accommodate changing network needs in a more efficient manner.